//
// PkzipClassic encryption
//
// Copyright 2004 John Reilly
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.
//


#if !NETCF_1_0

using System;
using System.Security.Cryptography;
using ICSharpCode.SharpZipLib.Checksums;

namespace ICSharpCode.SharpZipLib.Encryption
{
    /// <summary>
    /// PkzipClassic embodies the classic or original encryption facilities used in Pkzip archives.
    /// While it has been superceded by more recent and more powerful algorithms, its still in use and 
    /// is viable for preventing casual snooping
    /// </summary>
    public abstract class PkzipClassic : SymmetricAlgorithm
    {
        /// <summary>
        /// Generates new encryption keys based on given seed
        /// </summary>
        /// <param name="seed">The seed value to initialise keys with.</param>
        /// <returns>A new key value.</returns>
        public static byte[] GenerateKeys(byte[] seed)
        {
            if ( seed is null ) {
                throw new ArgumentNullException(nameof(seed));
            }

            if ( seed.Length == 0 ) {
                throw new ArgumentException("Length is zero", nameof(seed));
            }

            uint[] newKeys = {
                0x12345678,
                0x23456789,
                0x34567890
             };
            
            for (int i = 0; i < seed.Length; ++i) {
                newKeys[0] = Crc32.ComputeCrc32(newKeys[0], seed[i]);
                newKeys[1] = newKeys[1] + (byte)newKeys[0];
                newKeys[1] = newKeys[1] * 134775813 + 1;
                newKeys[2] = Crc32.ComputeCrc32(newKeys[2], (byte)(newKeys[1] >> 24));
            }

            byte[] result = new byte[12];
            result[0] = (byte)(newKeys[0] & 0xff);
            result[1] = (byte)((newKeys[0] >> 8) & 0xff);
            result[2] = (byte)((newKeys[0] >> 16) & 0xff);
            result[3] = (byte)((newKeys[0] >> 24) & 0xff);
            result[4] = (byte)(newKeys[1] & 0xff);
            result[5] = (byte)((newKeys[1] >> 8) & 0xff);
            result[6] = (byte)((newKeys[1] >> 16) & 0xff);
            result[7] = (byte)((newKeys[1] >> 24) & 0xff);
            result[8] = (byte)(newKeys[2] & 0xff);
            result[9] = (byte)((newKeys[2] >> 8) & 0xff);
            result[10] = (byte)((newKeys[2] >> 16) & 0xff);
            result[11] = (byte)((newKeys[2] >> 24) & 0xff);
            return result;
        }
    }

    /// <summary>
    /// PkzipClassicCryptoBase provides the low level facilities for encryption
    /// and decryption using the PkzipClassic algorithm.
    /// </summary>
    class PkzipClassicCryptoBase
    {
        /// <summary>
        /// Transform a single byte 
        /// </summary>
        /// <returns>
        /// The transformed value
        /// </returns>
        protected byte TransformByte()
        {
            uint temp = ((keys[2] & 0xFFFF) | 2);
            return (byte)((temp * (temp ^ 1)) >> 8);
        }

        /// <summary>
        /// Set the key schedule for encryption/decryption.
        /// </summary>
        /// <param name="keyData">The data use to set the keys from.</param>
        protected void SetKeys(byte[] keyData)
        {
            if ( keyData is null ) {
                throw new ArgumentNullException(nameof(keyData));
            }
        
            if ( keyData.Length != 12 ) {
                throw new InvalidOperationException("Key length is not valid");
            }
            
            keys = new uint[3];
            keys[0] = (uint)((keyData[3] << 24) | (keyData[2] << 16) | (keyData[1] << 8) | keyData[0]);
            keys[1] = (uint)((keyData[7] << 24) | (keyData[6] << 16) | (keyData[5] << 8) | keyData[4]);
            keys[2] = (uint)((keyData[11] << 24) | (keyData[10] << 16) | (keyData[9] << 8) | keyData[8]);
        }

        /// <summary>
        /// Update encryption keys 
        /// </summary>      
        protected void UpdateKeys(byte ch)
        {
            keys[0] = Crc32.ComputeCrc32(keys[0], ch);
            keys[1] = keys[1] + (byte)keys[0];
            keys[1] = keys[1] * 134775813 + 1;
            keys[2] = Crc32.ComputeCrc32(keys[2], (byte)(keys[1] >> 24));
        }

        /// <summary>
        /// Reset the internal state.
        /// </summary>
        protected void Reset()
        {
            keys[0] = 0;
            keys[1] = 0;
            keys[2] = 0;
        }
        
        #region Instance Fields
        uint[] keys;
        #endregion
    }

    /// <summary>
    /// PkzipClassic CryptoTransform for encryption.
    /// </summary>
    class PkzipClassicEncryptCryptoTransform : PkzipClassicCryptoBase, ICryptoTransform
    {
        /// <summary>
        /// Initialise a new instance of <see cref="PkzipClassicEncryptCryptoTransform"></see>
        /// </summary>
        /// <param name="keyBlock">The key block to use.</param>
        internal PkzipClassicEncryptCryptoTransform(byte[] keyBlock)
        {
            SetKeys(keyBlock);
        }

        #region ICryptoTransform Members

        /// <summary>
        /// Transforms the specified region of the specified byte array.
        /// </summary>
        /// <param name="inputBuffer">The input for which to compute the transform.</param>
        /// <param name="inputOffset">The offset into the byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the byte array to use as data.</param>
        /// <returns>The computed transform.</returns>
        public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
        {
            byte[] result = new byte[inputCount];
            TransformBlock(inputBuffer, inputOffset, inputCount, result, 0);
            return result;
        }

        /// <summary>
        /// Transforms the specified region of the input byte array and copies 
        /// the resulting transform to the specified region of the output byte array.
        /// </summary>
        /// <param name="inputBuffer">The input for which to compute the transform.</param>
        /// <param name="inputOffset">The offset into the input byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the input byte array to use as data.</param>
        /// <param name="outputBuffer">The output to which to write the transform.</param>
        /// <param name="outputOffset">The offset into the output byte array from which to begin writing data.</param>
        /// <returns>The number of bytes written.</returns>
        public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
        {
            for (int i = inputOffset; i < inputOffset + inputCount; ++i) {
                byte oldbyte = inputBuffer[i];
                outputBuffer[outputOffset++] = (byte)(inputBuffer[i] ^ TransformByte());
                UpdateKeys(oldbyte);
            }
            return inputCount;
        }

        /// <summary>
        /// Gets a value indicating whether the current transform can be reused.
        /// </summary>
        public bool CanReuseTransform => true;

        /// <summary>
        /// Gets the size of the input data blocks in bytes.
        /// </summary>
        public int InputBlockSize => 1;

        /// <summary>
        /// Gets the size of the output data blocks in bytes.
        /// </summary>
        public int OutputBlockSize => 1;

        /// <summary>
        /// Gets a value indicating whether multiple blocks can be transformed.
        /// </summary>
        public bool CanTransformMultipleBlocks => true;

        #endregion

        #region IDisposable Members

        /// <summary>
        /// Cleanup internal state.
        /// </summary>
        public void Dispose()
        {
            Reset();
        }

        #endregion
    }


    /// <summary>
    /// PkzipClassic CryptoTransform for decryption.
    /// </summary>
    class PkzipClassicDecryptCryptoTransform : PkzipClassicCryptoBase, ICryptoTransform
    {
        /// <summary>
        /// Initialise a new instance of <see cref="PkzipClassicDecryptCryptoTransform"></see>.
        /// </summary>
        /// <param name="keyBlock">The key block to decrypt with.</param>
        internal PkzipClassicDecryptCryptoTransform(byte[] keyBlock)
        {
            SetKeys(keyBlock);
        }

        #region ICryptoTransform Members

        /// <summary>
        /// Transforms the specified region of the specified byte array.
        /// </summary>
        /// <param name="inputBuffer">The input for which to compute the transform.</param>
        /// <param name="inputOffset">The offset into the byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the byte array to use as data.</param>
        /// <returns>The computed transform.</returns>
        public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
        {
            byte[] result = new byte[inputCount];
            TransformBlock(inputBuffer, inputOffset, inputCount, result, 0);
            return result;
        }

        /// <summary>
        /// Transforms the specified region of the input byte array and copies 
        /// the resulting transform to the specified region of the output byte array.
        /// </summary>
        /// <param name="inputBuffer">The input for which to compute the transform.</param>
        /// <param name="inputOffset">The offset into the input byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the input byte array to use as data.</param>
        /// <param name="outputBuffer">The output to which to write the transform.</param>
        /// <param name="outputOffset">The offset into the output byte array from which to begin writing data.</param>
        /// <returns>The number of bytes written.</returns>
        public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
        {
            for (int i = inputOffset; i < inputOffset + inputCount; ++i) {
                byte newByte = (byte)(inputBuffer[i] ^ TransformByte());
                outputBuffer[outputOffset++] = newByte;
                UpdateKeys(newByte);
            }
            return inputCount;
        }

        /// <summary>
        /// Gets a value indicating whether the current transform can be reused.
        /// </summary>
        public bool CanReuseTransform => true;

        /// <summary>
        /// Gets the size of the input data blocks in bytes.
        /// </summary>
        public int InputBlockSize => 1;

        /// <summary>
        /// Gets the size of the output data blocks in bytes.
        /// </summary>
        public int OutputBlockSize => 1;

        /// <summary>
        /// Gets a value indicating whether multiple blocks can be transformed.
        /// </summary>
        public bool CanTransformMultipleBlocks => true;

        #endregion

        #region IDisposable Members

        /// <summary>
        /// Cleanup internal state.
        /// </summary>
        public void Dispose()
        {
            Reset();
        }

        #endregion
    }

    /// <summary>
    /// Defines a wrapper object to access the Pkzip algorithm. 
    /// This class cannot be inherited.
    /// </summary>
    public sealed class PkzipClassicManaged : PkzipClassic
    {
        /// <summary>
        /// Get / set the applicable block size in bits.
        /// </summary>
        /// <remarks>The only valid block size is 8.</remarks>
        public override int BlockSize 
        {
            get => 8;

            set {
                if (value != 8) {
                    throw new CryptographicException("Block size is invalid");
                }
            }
        }

        /// <summary>
        /// Get an array of legal <see cref="KeySizes">key sizes.</see>
        /// </summary>
        public override KeySizes[] LegalKeySizes
        {
            get {
                KeySizes[] keySizes = new KeySizes[1];
                keySizes[0] = new KeySizes(12 * 8, 12 * 8, 0);
                return keySizes; 
            }
        }

        /// <summary>
        /// Generate an initial vector.
        /// </summary>
        public override void GenerateIV()
        {
            // Do nothing.
        }

        /// <summary>
        /// Get an array of legal <see cref="KeySizes">block sizes</see>.
        /// </summary>
        public override KeySizes[] LegalBlockSizes
        {
            get {
                KeySizes[] keySizes = new KeySizes[1];
                keySizes[0] = new KeySizes(1 * 8, 1 * 8, 0);
                return keySizes; 
            }
        }

        /// <summary>
        /// Get / set the key value applicable.
        /// </summary>
        public override byte[] Key
        {
            get {
                if ( key_ is null ) {
                    GenerateKey();
                }
                
                return (byte[]) key_.Clone();
            }
        
            set {
                if ( value is null ) {
                    throw new ArgumentNullException(nameof(value));
                }
                
                if ( value.Length != 12 ) {
                    throw new CryptographicException("Key size is illegal");
                }
                
                key_ = (byte[]) value.Clone();
            }
        }

        /// <summary>
        /// Generate a new random key.
        /// </summary>
        public override void GenerateKey()
        {
            key_ = new byte[12];
            Random rnd = new Random();
            rnd.NextBytes(key_);
        }

        /// <summary>
        /// Create an encryptor.
        /// </summary>
        /// <param name="rgbKey">The key to use for this encryptor.</param>
        /// <param name="rgbIV">Initialisation vector for the new encryptor.</param>
        /// <returns>Returns a new PkzipClassic encryptor</returns>
        public override ICryptoTransform CreateEncryptor(
            byte[] rgbKey,
            byte[] rgbIV)
        {
            key_ = rgbKey;
            return new PkzipClassicEncryptCryptoTransform(Key);
        }

        /// <summary>
        /// Create a decryptor.
        /// </summary>
        /// <param name="rgbKey">Keys to use for this new decryptor.</param>
        /// <param name="rgbIV">Initialisation vector for the new decryptor.</param>
        /// <returns>Returns a new decryptor.</returns>
        public override ICryptoTransform CreateDecryptor(
            byte[] rgbKey,
            byte[] rgbIV)
        {
            key_ = rgbKey;
            return new PkzipClassicDecryptCryptoTransform(Key);
        }
        
        #region Instance Fields
        byte[] key_;
        #endregion
    }
}
#endif
